The present invention concerns a passive restraining system for use in motor vehicles as well as an air bag module as restraining component, as it is preferably used in the passive restraining system.
Passive restraining systems for motor vehicles have been used in practice for a long time in multiple constructions. A restraining component of such a restraining system is an air bag, thus a gas sack which is inflated within fractions of a second in the event of an accident, in order to catch the trunk of the driver and/or passenger thrown forward by the impact. Such a restraining system including an air bag has available a so-called crash sensor, which in the event of an accident generates an appropriate signal which is then further processed by an evaluation electronics unit.
A crash sensor is usually a delay measuring device, that is, the negative acceleration is measured, which is basically stronger in the event of an accident than in normal braking of a motor vehicle in normal road traffic. If, among other things, the value of the negative acceleration exceeds a certain preset value, the evaluation electronics unit interprets this such that an accident has occurred, whereupon a prompting signal is generated to trigger a restraining component. The prompting signal causes, for example, a charge to be ignited, whereupon its explosion gases fill the gas sack. Another possibility is allowing a gas stored under pressure to expand into the gas sack after an activator has received an appropriate prompting signal.
Other known restraining components of a restraining system are so-called belt retractors, that is devices which tighten the safety belts in the event of an accident, in order to hold the persons in the wrecked vehicle more firmly in the vehicle seats.
Common to all known systems is that the reactions of the restraining components occur according to the classical either/or principle, that is, that the components react in only one predetermined manner after recognition of an accident situation by the crash sensor. The air bag thus only inflates and the belt retractor tightens the belt, and to be sure completely independently of whether further conditions are fulfilled. It is just this, however, which leads to problems in practice. Let it be mentioned here, for example, that fatal incidents can transpire owing to the either/or principle if, for example, a so-called reboard child's seat is placed on the passenger seat and is fastened there by means of the safety belt. In the event of an accident, the inflation of the passenger air bag can represent a lethal danger for the child sitting or lying on the seat. It is also evident that the standard reaction of a restraining component, for example the air bag, cannot be equally optimal for persons of different body weight or different body circumference. Traditional systems and components are thus not flexible, wherein a serious disadvantage of known systems is seen.
Passive restraining systems are described in the patent literature, for example, in U.S. Pat. No. 5,413,378 and DE-A-41 12 579. All these devices have a central control device which is supposed to undertake the task of collision recognition, signal preparation and transmission. However, if this device itself is damaged by the impact, a total failure of the restraining system can take place with full consequences for the motor vehicle occupants. Nothing else would apply for the safety device in accordance with DE-A-38 1 217, much less for the air bag system in accordance with WO 95/11819, according to which an electronic control unit controls the operation of a multiple stage gas generator dependent upon various signals detected by sensors.
Indeed, it is known, for example, from DE-Z-"Sensor Technology," Springer Publishing Company 1992, W. Heywang to arrange a series of sensors, which form part of a network, in a decentralized manner. This alone, however, does not suffice with respect to the special requirements for a passive restraining system in a motor vehicle to guarantee the safety of the vehicle occupants, as long as namely a central control device is provided, as described in the above-mentioned publications.